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Sickle Cell Test

Test Overview

A sickle cell test is a blood test done to
check for
sickle cell trait or
sickle cell disease. Sickle cell disease is an
inherited blood disease that causes red blood cells to be deformed (sickle-shaped). The red blood cells deform because
they contain an abnormal type of
hemoglobin, called hemoglobin S, instead of the normal
hemoglobin, called hemoglobin A.

Sickled blood cells are
destroyed by the body faster than normal blood cells. This causes
anemia. Also, sickled cells can get trapped in blood
vessels and reduce or block blood flow. This can damage organs, muscles, and
bones and may lead to life-threatening conditions.

The best way
to check for sickle cell trait or sickle cell disease is to look at the blood
using a method called high-performance liquid chromatography (HPLC). This test
identifies which type of hemoglobin is present. To confirm the results of HPLC,
a
genetic test may be done.

Sickle cell
disease is an
autosomal recessive disease. This means that to have
the disease, a person must inherit a
gene for the disease from both parents. Each person
inherits two genes (one from each parent). As a result, a person may
have:

Two genes that make normal hemoglobin
(hemoglobin A). These people have normal red blood cells, unless they have some
other disease.

One gene that makes hemoglobin A and one that makes
hemoglobin S. These people carry the sickle cell trait (and are called "a
carrier"), but they do not have sickle cell disease.
Sickle cell trait is usually a harmless condition.

Two genes that
make hemoglobin S. These people have sickle cell disease. Both parents either
carry the sickle cell trait or have the disease. Sickled red blood cells often
cause recurring health problems called
sickle cell crises.

One gene that makes
hemoglobin S and one that makes some other abnormal type of hemoglobin.
Depending on the other type of abnormal hemoglobin, these people may have mild
or severe
sickle cell disorder.

Why It Is Done

A sickle cell test is done to help diagnose sickle cell disease.

A sickle cell test is also done to screen for sickle
cell trait or sickle cell disease. This test may be done for newborns and for people at high risk. Detecting sickle cell
trait is important for couples who want to have children and who may be
carriers of sickle cell trait.

How To Prepare

Be sure to tell your doctor if you have had a
blood transfusion in the past 4 months because it can
interfere with the test results.

How It Is Done

Blood sample from a vein

The health professional drawing blood will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure to the site and then a
bandage.

Blood sample from a heel stick

During newborn testing, the blood sample is usually
taken from your baby's heel (called a heel stick).

Your baby's heel is cleaned with alcohol and then the heel is
poked with a small needle.

Several drops of blood are collected
inside circles on a special piece of paper.

When enough blood has
been collected, a small bandage is put on the site.

How It Feels

The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.

Your baby may feel a sting or a pinch with a heel
stick.

Risks

Blood sample from a vein

There is very little chance of a problem from having
a blood sample taken from a vein.

You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.

Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (such as Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.

Blood sample from a heel stick

Usually, there are no problems from a heel stick. A
small bruise may develop. Babies with bleeding problems may bleed more with
usual. Sometimes bleeding problems are found when blood is being collected for
the sickle cell test.

Results

In sickle cell trait, more than half of
the hemoglobin is normal (hemoglobin A) and less than half is abnormal
(hemoglobin S).

In sickle cell disease, almost all hemoglobin is
hemoglobin S with some hemoglobin called
hemoglobin F.

In babies, a sickle cell blood test may be repeated at 6
months old, or a genetic information (DNA) test may
be done.

What Affects the Test

Having a blood transfusion in
the past 4 months can cause a
false-negative test result because of the normal
hemoglobin from the blood donor.

What To Think About

Most states routinely do a sickle cell blood
test on all newborns.

If you have a family history of sickle cell
disease, you may be advised to have a blood test to determine whether you carry
the sickle cell trait. If you have sickle cell trait or sickle cell disease,
you may choose
genetic counseling before deciding to have
children.

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